From: Stephen Hemminger <stephen@networkplumber•org>
To: anirup dutta <adutta2@uh•edu>
Cc: netdev@vger•kernel.org
Subject: Re: Netem Delay Normal Distribution
Date: Sun, 27 Oct 2013 12:37:01 -0700 [thread overview]
Message-ID: <20131027123701.7581550b@nehalam.linuxnetplumber.net> (raw)
In-Reply-To: <CAJx7G_xkrVkC7HGQZogivA_6-i2Gas6aJd-sOFNMEbmq8=cS0g@mail.gmail.com>
On Sat, 26 Oct 2013 21:31:03 -0500
anirup dutta <adutta2@uh•edu> wrote:
> Hello,
>
> I try this on my device
>
> sudo tc qdisc del dev eth0 root netem delay 100ms 20ms distribution normal
>
> I use iperf for transmitting UDP packets and I modified its code to
> get per packet delay. When I plot the distribution of delays and
> analyze the delays they pass the normality tests.
>
> The only problem that I am not able to understand is that the mean of
> those delays shift to 125ms. Its not only me. There was another study
> and it observed the same thing.
>
> http://www.researchgate.net/publication/224256550_An_Empirical_Study_of_NetEm_Network_Emulation_Functionalities/file/d912f5058c9b1e409b.pdf
>
> Figure 7
>
> I found out that this command is valid
>
> sudo tc qdisc del dev eth0 root netem delay 1ms 20ms distribution normal
>
> So I have a feeling that mean gets shifted from the base delay to
> avoid negative delay values.
>
> It would be great if someone can confirm how it is implemented?
The table distribution logic actually predates netem.
It came from NIST Net http://snad.ncsl.nist.gov/nistnet/
The code was direct copy from this public domain code.
prev parent reply other threads:[~2013-10-27 19:37 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-27 2:31 Netem Delay Normal Distribution anirup dutta
2013-10-27 19:27 ` Eric Dumazet
2013-10-27 19:37 ` Stephen Hemminger [this message]
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